int exgcd(int a,int b,int &x,int &y)
{
	if(b==0)
	{
		x=1;
		y=0;
		return a;
	}
	int d=exgcd(b,a%b,x,y);
	int t=x;
	x=y;
	y=t-a/b*y;
	return d;
}
